CFD Hydrodynamics Forces Determination for a Darrieus Turbine Rotating Blades Using K-ε Turbulence Model

Abstract

Determinationof hydrodynamic forces acting on the blades of Darrieus turbine used to harnesswater energy from dams, rivers and ocean is very important to evaluate thisturbine performance. Therefore, this paper presents the numerical results ofCFD investigation using K-ε closure turbulence model. This simulation has beenperformed for a hydro Darrieus turbine that we have previously testedexperimentally; this turbine has a diameter of 21.5 cm and it is composed ofthree NACA0020 blades, with a height of 23 cm and a cord of 7 cm, that arefixed with a separation angle of 120 °. The present simulation has been carriedout for a water flow velocity of 0.67 m/s and the Darrieus turbine rotatingvelocity of 125 rpm. These values correspond to a specific velocity λ equal to2, a flow Reynolds number Rev equal to 4.57 104, a rotational Reynolds numberReu equal to 1.97 105 and a relative Reynolds number Rew varying between 4.72104 and 1.39 105. The graphical presentations of the simulation numericalresults have shown practically identical curves, respectively for thehydrodynamic lift and drag forces variations versus the rotational angle(position angle of each blade) with a phase angle of 120° between the firstblade and the second one and of 240° between the first blade and the third one.The hydrodynamic blade element lift force varies between 0.0454 and 0.641 Nwhile the drag force varies between - 0.0968 and 0.342 N. The global turbine hydrodynamiclift and drag forces (for the three blades elements together) variesrespectively between 0.5928 and 0.9251 N and between 0.0335 and 0.2497 N. Themaximal values show that the lift is about twice the drag for each blade andabout four times for this turbine. The turbine average lift and drag forcesover three rotations are respectively 32.38 N and 6.61 N.